Computer-aided design of evanescent mode waveguide bandpass filter with nontouching E-plane fins

CAD of evanescent-mode bandpass filters based on the short ridged waveguide sections

“…These filters may be realized with the Eplane screws [1][2][3] but their application requires a time-consuming filter tuning and is problematical at the millimeter-wave range. Application of nontouching E-plane fins of a small thickness [4,5] and metal-finned or ridged WG short sections [6][7][8][9][10][11][12] led to "tuning-less" technology and provided the possibility of low-cost fabrication. At present, there are many papers in which various methods for the exact determination of the transverse electrical (TE) and transverse magnetic (TM) modes in the ridged WGs have been developed and have been compared.…”

“…As a rule, an initially synthesized filter has a passband much wider than the specified one. Sometimes, this step was simply excluded from the design procedure or, as in [5], was replaced by the previously calculated look-up table for the scattering parameters of single fins, because the authors of [5] could not find a suitable relationship between the equivalent circuit elements of a short fin and its dimensions. A partial solution of the problem was found in [8] where quarter-wave resonators were used.…”

“…Usually, a below-cutoff filter housing is chosen to be one of the standard rectangular WGs, the cross section of which is smaller than that of the main WG [4][5][6][7][8][9]. To reach a wider highfrequency stopband, a smaller filter housing width and a narrow ridge gap have to be chosen.…”